End fire element array



Jan. 2, 1962 R. D. B OGNER END FIRE ELEMENT ARRAY 3 Sheets-Sheet 1 FiledJuly 29, 1957 END FIRE RADIATORS FIG.I

FIG. 2

'90 -75 -6O '45 -3O -l5 9 (ANGLE FROM BEAM PEAK IN DEGREES) INVENTOR.

RICHARD D. BOGNER AGENT Jan. 2, 1962 R. D. BOGNER 3,015,821

END FIRE ELEMENT ARRAY Filed July 29 195'? 3 Sheets-Sheet 2 FIG. 3

F I G. 6

FIG. 8

50 5| 52 53 L 5|, 5s 51 53 E mmvrox.

RICHARD 0. BOGNER BY prwmx AGENT Jan. 2, 1962 R. D. BOGNER 3, ,8

END FIRE ELEMENT ARRAY Filed July 29. 195'? 5 Sheets-Sheet 3 INVENTOR.

AGENT vRICHARD D.. BOGNER FIG. 5

L i i United States Patent ()1 3,015,821 END FIRE ELEMENT ARRAY RichardD. Bogner, Bethpage, N.Y., assignor to Avien, Inc., Woodside, N.Y., acorporation of New York Filed July 29, 1957, Ser. No. 674,926 9 Claims.(Cl. 343-453) This application is a continuation in part of my copendingapplication entitled Antenna, Serial No. 631,869, now Patent No.2,955,287, filed Dec. 31, 1956 and assigned to the assignee of thisapplication. i

This invention relates to directional antennas.

In the design of directional antennas, the general considerationsinclude as a goal the obtaining of high gain, narrow beam width and lowside lobes. These desideratums are generally not achievedrin fullbecause of practical considerations of weight, size or mechanicallimita-, tions. An antenna design frequently requires compromise of bothmaximum desired side lobe level and maximum desired beamwidth at thehalf power level, in a given plane, for an antenna of a givenmaximum'physical size. In some applications, the designer mayberequiredto accept a more moderate gain in order to achieve lower side lobelevels, or compromise all. Characteristics because of sizeconsiderations. I g

It .is often required in the design of antennas especially, for example,large rotating antennas, that the diameter of a circle whichcircumscribes the antenna in a plane normal to the rotation axis beminimized for a given radiationpattern, half power beamwidth and sidelobe level in that plane. This plane is often the plane of largestantenna linear dimension and is usually the azimuth plane. Y

An antenna structure is described herein which. requires a smallercircumscribed diameter for a given half power beamwidth and side lobelevel, than has previously been considered practical to obtain. t

I have discovered that by properly arranging a number of end fireelements inan array I can achieve an antenna pattern of narrowerbeamwidth consistent with a given side lobe level, in a smaller antennadiameter than was previously considered practicable. Briefly stated,-the antenna of this invention consists of an integral number ofsubstantially identical end fire radiators arranged in an equally spacedarray. The spacing between elements, the length of the elements, thenumber of elements and other critical dimensions-are so chosen inaccordance with the procedure stated more fully hereinafter that for agiven circumscribed diameter an antennaof surprisingly high gain, orsurprisingly narrow beamwidth for agiven low side lobe level, isobtained in a compact structure. 1 i

There follows hereinafter a mathematical analysis of the antenna-whichestablished a preferred range of con figurations providing optimumperformance.

It is a general object of this invention to provide a high gaindirectional antenna having a narrow half power level beamwidth and lowside lobe level in relation to the diameter of a circumscribed circle.

It is another object of this invention to provide a directional antennaof small height and breadth for a given value of antenna gain.

It is still a diiferent object to provide a high gain directionalantenna of small weight.-

A further object of this invention is to provide a high gain directionalantenna characterized by very low side lobe levels. a

A still different object of this invention is to provid an improvedantenna of high performance characteristics susceptible of beingembodied in a rigid mechanical structure.

3,015,821 Patented Jan. 2 1962 ice A further object is to provide anantenna capable of being simply and quickly assembled and disassembledby relatively unskilled personnel.

These and other objects, the nature of the present invention, itsvarious features and advantages, will appear more fully uponconsideration of the various specific illustrative embodiments shown inthe accompanying drawings and of the following detailed descriptionofthese embodiments.

In the drawings:

FIGURE 1 shows in plan an antenna array of this invention. v

FIGURE 2 is a rectangular plot of a measured typical field strengthpattern (in db) propagated by a four equally fed element antenna ofthis'invention which is four wavelengths in diameter in the plane of thearray.

FIGURE 3 is a pictorial representation of a single element of an arrayof this invention wherein the element utilizes a flat supporting rod andrectangular wire mesh discs. The element is shown energized by a dipolelauncher.

FIGURE 4 is a pictorial representation of a portion of an array of thisinvention utilizing a round support rod and round discs energized by awave-guide launcher. FIGURE 5 is a general schematic showing in plan ofa four element array of this invention employing a di-' pole launchedcigar element.

FIGURE 6 shows in plan the projection in a vertical plane of theelements of a fourarray antenna.

FIGURES 7, 8 and 9 show in schematic form, the side, front and planviews respectively of another antenna array.

As employed hereinafter the term degrees refers to electrical degrees.The linear dimensions are stated as relative values throughout, relativeeither to one wavelength or to 360 electrical degrees (which isequivalent to one wave length) of the operating frequency. A lengthstated as 2 for example, means either two wave lengths or two (360)equal to 720 electrical degrees.

The structure consists of an n number of substantially identical endfire radiators 2a, 2b, 2c, etc., of length L and end width w, arrangedin an equally spaced array and inscribed in a circle 4 of diameter d.The spacing between elements is s, and the distance from the center ofthe end radiator 2a to the furthest edge of the ground plane 6 is A.Since the width of the resulting radiation beam (FIGURE 2) is an inversefunction of both the pro-duct ns, and the square root of the length L,this beam will be narrowest for given d when both L and ns are made aslarge as possible. The circumscribed circle of diameter d referred to isdefined by four points, the outside corners of the end radiators 2a and2e and the edges of the ground plane. There exists simple plane geometryrelationship as shown ni FIGURE 1 which .may be expressed as amathematical relationship between L, d, w, A, n and s (or between L andthe product (n- -l)s for a fixed a, A, and w, the latter two valuesbeing small and relatively constant in a practical system), based onsimple plane geometry relationships in conjunction with FIG-- URE 1which relationship is A second and separate relationship can be set upbetween L and its if the required condition of low side lobes is to bemet with the minimum diameter d. In general, it is desirable to maximizens within the circle consistent with an L just large enough to give theside lobe level required, since L must be larger, in most cases, for agiven element factor beamwidth, base length is defined as the distancebetween center lines of end elements and is- (n1)s for n elements thanthe base length (n-l)s for a given array factor beamwidth.

I-Equal amplitude feed embodiment For the casein which each of theelements of the array is fed with substantially the same amplitude ofsignal, side lobe levels of the entire antenna in the order of 22 to 26dbbelow the beam peak level in the plane of interest can be obtained.For this situation, the required relationship between L and us can bedetermined from the fact that the shortest value of L giving rise to2226 db side lobes has been found to occur when the angular displacementof the first element pattern null from the beam peak (6 is between 63%and 84% greater than the displacement of the first array factor nullAdding to this the two known facts that (l) for close to optimallydesigned end fire elements, having 8-l3 db first (maximum) side lobes, 0lies between 40 and 50 times the reciprocal of the square root of L, andthat (2) the array factor null occurs at 180 divided by ns for ns 2 /2,the required range of L in terms of as can be found as follows:

Substituting (3) and (4) in (2) and solving for the maximum and minimumsimultaneous extremes of (2) and (3):

1 2 emf S S 0 Equation 5 and the mathematical relationship previouslydescribed between L and (nl)s [Eq. 1] allow a mathematicaldeterminationof a range of the number of elements, their spacing and length requiredto make optimum use of the area of the circle of diameter d. The valuesof w and A, as well as the exact function between the length L of theend fire element and the position of the first end fire element patternnull 0 must be known in any particular case for an exact solution; sinceit is desirable to have a mini-mum w and A, and since also the range ofthe optimum relationship between L and 0 is well known as described,however, the structure may in generalbe determined within narrow anddefined limits.

Simultaneous solution of Eq. 1 and Eq. 5 over the range of the lattershow that this antenna design provides adistinct advantage overconventional techniques in terms of obtainable beamwidth for 2226 dbside lobe levels in a given diameter d. This advantage, however, isshown by the solutions to occur only in the range of d between 2 and 12wavelengths, which requires a range of n between 2 and 16.

It was stated in my above referenced copending application that theelement spacing was restricted to the range of 160 to 320 electricaldegrees. The basis of the lower limit was, and still remains, highmutual coupling and physical size of the elements, which are around 120'degrees'wide. The basis of the upper limit of 320. degrees was creationof high side lobes at large angles off the beam peak due to both thearray factor characteristic, and the fact that the element side lobesare usually high. The total pattern is the product of array and elementfactors. The array factor characteristic states that this factor reachesa maximum value (unity) at other angles in addition to 6:0, the normalto the array, when the spacing s becomes equal to or greater than 360degrees. A high element side lobe level is especially evident for thecase of horizontal polarization (the common radar and scatterpropagation case). where the element pattern often has a high level outto the region of 90 degrees off the peak (0:90). In fact, this leveloften remains high after the first side lobe, and in the order of 16 dbbelow the peak. An improvement of only about 6 db is realized at 90degrees using a 320 degree element spacing, giving a 16+6=22 db productside lobe at 90 degrees. This side lobe level (22 db) was stated asbeing the maximum tolerable for the uniform amplitude case. (Even lowerside lobe levels are necessary for the tapered amplitude case.) This 320degree limitation is therefore completely safe and generally necessary.

It has been discovered, however, that if the element pattern does inspecial cases offer lower second and succeeding side lobe levels, theallowable maximum spacing can be made larger than 320 degrees with lowproduct side lo-bes maintained. As shown previously, the largestpossible spacing is the most desirable as regards meeting the objectivesof maximum obtainable gain within a given swing circle and of minimummutual coupling between and among elements.

Two slightly different cases of element pattern are disclosedhereinafter which may allow larger spacing.

in case I, the level of the element pattern never rises higher than 22db below the peak level anywhere beyond the first side lobe. In thiscase a secondary (or higher order) array factor unity value can beallowed to occur (by virtue of element spacing equal to or greater than360 degrees) at any angular position between 0:90 degrees and 6:0 (0 isdefined as the angle between the beam peak,.or the array normal where0:0, and the 22 db level on the side of the first element side lobefurthest from the beam peak.)

In case 11, the second element side lobe does rise above 22 db, but thethird and succeeding side lobes are low. Here the array factor unity andthe second side lobe peak cannot be allowed to be coincident, but a lowproduct side lobe can still result if a second array factor unity occursnear the null between the first and second element side lobes. Becauseof the array factor and element factor side lobes are of the same orderof angular width in this design, it is improbable that the produut sidelobe level will rise above 22 db with the restrictions on elementpattern stated for case II.

In both cases, therefore, the same criterion can be imposed to determinemaximum allowable spacing: the sec ond array factor unity value cannotin general occur any closer to the beam peak than the angular positionof the 22 db level on the side of the first element side lobe nearestthe second element side lobe. For practical purposes, the position ofthe null between the first and second ele-.

1 ment side lobes can be used to replace the 22 db level,

since the angular separation between these 2 positions is extremelysmall.

It 'must be re-empha-sized before proceeding that this increased angularspacing is only tolerable if the element pattern displays thelow levelsbeyond the first side lobe described as necessary, simultaneous with thenarrow first null-width with respect to length stated originally as arequisite for gain improvement using this technique. In general only thecigar and certain other retarded surface wave type end fire elementshave been observed in certain cases to exhibit this combination ofcharacteristics,

Use of spacings in the range 320 degrees to Sill-T 1/1 degrees istherefore restricted to embodiments employing the cigar end fire elementin one of its various forms. The angle between the array normal and thesecond unity value of the array factor is H=arc sin[21r/S](Eq. 6) wheres is the element spacing. This angle 0 is degrees at S=21r=360 degrees,and decreases toward 0:0 as S becomes larger. This angle 0 must beequated to the angle 0 referred to previously. It can be foundempirically that 0 ==4fl where 0:13 was defined to be the angularposition of the element half power level. Therefore, substituting:

where S is the maximum spacing in radians.

I However, t

, vi i -4r degrees as stated previously.

Therefore,

S =360/sin 9: degrees (8) Equation 8 defines the maximum allowablespacing S in degrees as a function of L, the element length inwavelengths. This spacing is 560 degrees for L=4, and 431 degrees forL=2, for example. 7

The increase in range of allowable spacing for this restricted type ofelement is therefore between [320] degrees and a 360 sin 7 lv ,Zdegrees, whereas previously the range was {160] to [-3 degrees-- 3 Basedon the foregoing relationships and experimental data, the followinglimitations have therefore been found critical; for-the case" ofsubstantially-equal amplitudes (or 22-26 db side lobe levels):

1. sh lbe be we .x a m t sj'shall be between l60 and 320electricaldegrees in'general, and between 160 and 360/ 80 .SlIl

" degi'ees'for elements falling in 'the general classnof (where L andsare in wavelengths). n shall be between 3 and 15 in number. Arepresentative'set of solutions for d=4 (wavelengths),

are found from Eq. 1, 2, 3 and 4 to be:

and %(TLS)2 The values of d, 6 0 A and w chosen above are onlyrepresentative of choices in the allowable ranges of these parameters,showing that a discrete solution for n, s and L is then possible. Smallvariations in the relationships between 0 and 0 and 0 and L, required inany case will cause small changes in the values of S and L for a given dand n.

II-Tapered amplitude feed embodiment in the limit. Forany particularside lobe level desired,

L between Vs (ns) and /2 (ns) I I s shall be between 160 and 320electrical degrees in general, and between 80 and 360 SlIl de rees g forelements falling in the general class of cigars. n between 3 and 18 dbetween 2k and 15 Suitable end fire radiators include in generalhelices, dielectric rods such as polyrods and ferrods and cigars,

except for therange of s above 320 degrees, where only cigars have beenfound suitable.

' .The cigar class of elements as shown illFIGURES- 3," 4 and 5 arepreferred for linearly polarized radiation for any spacing.Experimentally, it 'has' been-found that the cigar-type elements aloneallow metallic support along their lengths in the'fo'rm of thin rodsnormal to the prin-- cipal polarization electric vector; eliminating theneed forv long cantilevered structures and providing extremely rigidmechanical structures. Further, such an all metallic structure has beenfound lower in loss than structures in-f volving use of dielectrics. Thecigars, therefore, provide a distinct and incontrovertible advantage.both'in gain, weight and mechanical rigidity. r

' A typical structure is shown in FIGURE 4 wherein the cigar elementsmay consist of a cylindrical rod 29 and mounted thereon a plurality ofdiscs 22. The discs 22 are spaced approximately /s)\' to /2 apart andare approximately Mm to /2k in diameter. When the radiator of length L(L is expressed in wavelengths of operating frequency) is energized by alauncher such as a wave-- guide cavity 24, the electrical length L ismeasured from the feed 28 to the effective end (the end disc 46). Aminor protrusion of rod 20 may be disregarded.

In FIGURE 5 there is shown schematically a similar cigar element arrayfed by means of a dipole. In this instance the length L is measured fromthe dipole ele ment 26 to the effective end (disc 48). a

The structure is adapted to extremely simple and rigid mechanicalconstruction. Pedestal 30 which may be of a rotating type supports theantenna by means of arms 32, 34, and 36. Beam 35, in turn, supports theother cigar elements by means of a similar arm arrangement.

The transmission line structure used to feed the elements may consist ofa series of bilateral or other parallel splits, a series feedarrangement, or any other which provides the required amplitude, phase,and impedance with adequate decoupling.

The various elements or radiators 2a, 2b etc., shall be fedsubstantially in phase. The end elements may in certain cases bemodified slightly from the other elements to reduce the diameter d, sucha small alteration in certain cases not appreciably disturbing theperformance.

Septa, chokes, or metal plates may in some cases be placed around orbetween the bases of the elements to reduce or alter mutual couplingeffects.

Typical uses for the antenna include object location, communication,scatter propagation, and object detection.

The array of this invention may be stacked in multiple to provide abattery of such arrays providing a desired pattern in the verticalplane, controlled by the relative pointing, phase or amplitude of thebanks.

The ground plane 61 may be solid metal or may be in the form of anexpanded wire mesh or screen in order to reduce weight. Likewise asshown in FIGURE 3 the discs may be formed of wire mesh.

FIGURE 3 shows a dipole 62 feeding rectangular discs 63 formed of wiremesh. The support is a flat member 65 rather than a rod.

While I have chosen to show a balanced feed dipole structure in FIGURE 3fed by balanced input line 64, it is to be understood that aconventional unbalanced feed utilizing a balun may be employed.

It is not intended to imply that Support rod need be of metal: It may beof a dielectric material such as glass fiber impregnated with epoxyresin. The discs may consist of solid metal, or wire mesh, or simplerods, and may be of any shape symmetrical about a plane normal to theplane of interest and containing the axis of the metal rod. The spacingbetween discs will be between /s)\ and /2)\, and the disc width in theplane of interest also between /s7\ and VA.

FIGURE 6 shows in plan the projection in a vertical plane of theelements of a four array antenna.

A typical antenna consisting of four arrays, 40, 41, 42, and 43 is shownin FIGURE 6. The number of elements in all arrays need not be identicalbut may be varied to shape the resulting pattern. In general, thebeamwidth of each array should be approximately the same.

There is shown in FIGURES 7, 8, and 9 respectively, in schematic form,the side, front, and plan view of an antenna array in which theradiating elements .50 and 52 are tilted with respect to elements 51 and53. In embodiments employing tilted elements it is important that themeasurements of element length and spacing be that of the projection ofthe element onto the plane common to the elements.

What I claim is:

1. A high gain antenna for transmission of energy of wavelength xcomprising a plurality of retarded surface wave end fire elements, eachof said elements being composed of a plurality of discrete metallicmembers, each said member being greater than M4 and less than M2 inmajor dimension, each said member being symmetrical about a planecontaining an axis common to said members, said members being spacedbetween M8 and M2 apart along said axis, said axis being aligned in thedirection of propagation of said element to form an elongated radiatorfitting within a circumscribing cylinder coaxial withsaid axis, saidcylinder having a diameter which is greater than M4 and less than M2,said elements being arranged so that their projections onto a commonplane are parallel; a launcher arranged symmetrically about said axisfor propagation of energy along said axis and means for feeding saidlaunchers in common phase, said elements being spaced at leastelectrical degrees apart 3. The antenna of claim 1 wherein said elementsare.

equally spaced.

4. The antenna of claim 1 wherein said discrete metallic members areuniformly spaced along said common axis.

5'. A high gain antenna for transmission of energy of wavelength x,comprising a plurality of retarded surface wave end fire elements, eachof said elements being composed of a plurality of discrete metallicmembers, each said member being greater than M4 and less than M2 inmajor dimension, each said memberbeing symmetrical about a planecontaining an axis common to said members, said members being spacedbetween M8 and M2 apart along said axis, said axis being aligned in thedirection of propagation of said element to form an elongated radiatorfitting within a circumscribing cylinder coaxial with said axis, saidcylinder having a diameter which is greater than M4 and less than M2,said elements being arranged so that their projections onto a commonplane are parallel; a launcher arranged symmetrically about said axisfor propagation of energy along said axis and means for feeding saidlaunchers in common phase; said elements being spaced between I to 1966electrical d g sin VI sin References Cited in the file-of this patentUNITED STATES PATENTS 2,419,205 Feldman Apr. 22, 1947 2,556,046 SimpsonJune 5, 1951 2,588,610 Boothroyd et al Mar. 11, 1952 2,663,797 Koch Dec.22, 1953 2,684,725 Kock July 27, 1954 2,820,221 Broussaud Jan. 14, 1958FOREIGN PATENTS T8447 Germany Aug. 2, 1956 VIIIa/21a 732,827

Great Britain June 29, 1955 OTHER REFERENCES Kock and Harvey: APhotographic'Method for Displaying Sound Wave and Microwave Patterns,Wireless Engineer, August 1951, pages 564 to 587 (page 581' relied on).

